Effects of Exogenous Addition of L-Proline on the Occurrence of Cotton Verticillium Wilt and Its Soil Microbial Community in Rhizosphere
[Objective]Root exudates are signal mediators for the interaction between plants and soil microorganisms,which have important regulatory functions for plant disease occurrence and plant growth.The objective of this study is to clarify the microecological mechanism of L-proline in root exudates of cotton against the occurrence of Verticillium wilt,reveal the relationship of L-proline-mediated interaction between rhizosphere microorganisms and the occurrence of cotton Verticillium wilt,and to provide a new perspective for the construction of beneficial bacterial communities for the biological control of soil-borne diseases.[Method]Through greenhouse pot experiments,different concentrations of L-proline(0,50,100,200,and 400 mmol·L-1)were set as experimental treatments,and real-time fluorescence quantitative PCR and metagenomic sequencing techniques were used to determine the DNA copy numbers of Verticillium dahliae and microbial community structure and function of soil samples treated with L-proline.The microbial community structures of rhizosphere soils under different concentrations of L-proline were compared using principal component analysis.Redundancy analysis was used to study the correlations between soil nutrient factors and microbial community structure,and Spearman correlation analysis was focused on the relationships between microbial community structure and functional metabolic pathways.[Result]Compared with the blank control,the occurrence of cotton Verticillium wilt could not reduce under low concentration(50 mmol·L-1)L-proline treatment,while the disease indexes under high-concentration(100,200,and 400 mmol·L1)L-proline treatments were decreased by 22.51％,60.23％,and 64.23％,respectively.The results of qPCR showed that L-proline treatment did not significantly decrease the copy numbers of V dahliae in soil.The metagenomic sequencing analysis showed that the Shannon index of bacterial diversity significantly increased after L-proline treatment,while the Shannon index of fungal diversity showed a downward trend.At the genus level,the relative abundances of Nocardioides,Lysobacter,Arthrobacter,Phycicoccus,Pseudomonas,and Mucor were increased after treatment with L-proline.Linear discriminant analysis(LDA)showed that the enrichment of microbial KEGG pathways in rhizosphere soil changed after exogenous addition of L-proline,except for L-proline at the concentration of 100 mmol·L-1.Redundancy analysis showed that bacterial community composition was significantly influenced by pH,conductivity,nitrate nitrogen,ammonium nitrogen,and organic matter(OM),while fungal community composition was significantly correlated with ammonium nitrogen.Spearman correlation analysis showed that the bacterial KEGG pathways were negatively correlated with pH,OM and ammonium nitrogen,while positively correlated with conductivity and nitrate nitrogen.Most of the KEGG pathways of fungi had poor correlation with soil nutrients.[Conclusion]The exogenous addition of an appropriate amount of L-proline can influence the occurrence of cotton Verticillium wilt through altering the structure and function of soil bacterial communities,increasing the relative abundance of beneficial microorganisms,but it cannot change the DNA copy numbers of pathogen.Meanwhile,the composition and function of bacterial community are related to soil nutrients.
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